Metal oxide-hydrogen batteries, such as nickel oxide-hydrogen batteries, have seen use as aircraft starter batteries and in aerospace applications, because they are rechargeable, have an extremely long cycle life and provide a uniform output during the entire discharge cycle.
In the typical nickel oxide-hydrogen battery, the battery cells are sealed in an outer pressure vessel that contains pressurized hydrogen gas. On discharge of the battery, the hydrogen gas diffuses through the electrolyte surrounding the catalyst surfaces of the negative plates and becomes disassociated to the mono-atomic form. The mono-atomic hydrogen is ionized and combines with hydroxyl ions to form water with an electron being released in the process of forming each hydrogen ion. In addition, hydroxyl ions are formed at the positive electrode by the reaction of water with the available oxygen content of the nickel oxide. As a result of these reactions an electron current is produced in the exterior circuit.
On recharging, the reaction is reversed, with the recharging being characterized by the regeneration of hydrogen at the negative electrode and the reoxidation of the nickel hydroxide at the positive electrode.
In practice, the exterior electrical connection is made to the battery cells after the outer pressure vessel is formed around the cells. A common technique has been to form single polarity termination stems at each end of the vessel which are sealed within openings in the opposite heads of the vessel.
In certain instances in order to accommodate the user's requirements, a coaxial termination assembly would be desirable in which both the negative and positive poles exit at the same end of the vessel. For example, in an aircraft starting battery, the battery normally contains an external plug-in connection and to accommodate the plug-in connection it would be advantageous to have a coaxial battery termination in which both poles extend in coaxial relation through a single end of the pressure vessel. If the poles exit from opposite ends of the vessel, at least one of the external conductors leading to the plug-in connection would have to have a substantially increased length which could detract from the performance of the battery, as well as increasing the overall battery length which is a critical factor in certain applications having limited space, such as aircraft starting applications.